“Conscience is better served by a myth.”

Widely attributed to Leo X, the earliest known source of this statement is actually a polemical work by the Protestant John Bale, the anti-Catholic Acta Romanorum Pontificum, which was first translated from Latin into English as The Pageant of the Popes in 1574: "For on a time when a cardinall Bembus did move a question out of the Gospell, the Pope gave him a very contemptuous answer saying: All ages can testifie enough how profitable that fable of Christe hath ben to us and our companie." The Pope in this case being Leo X. Later accounts of it exist, as recorded by Vatican Librarian, Cardinal Baronius in the Annales Ecclesiastici (1597) a 12-volume history of the Church.
In a more modern polemic, "The Criminal History of the Papacy" by Tony Bushby, in Nexus Magazine Volume 14, Number 3 (April - May 2007) http://www.bibliotecapleyades.net/vatican/esp_vatican30c.htm, it is stated that "The pope's pronouncement is recorded in the diaries and records of both Pietro Cardinal Bembo (Letters and Comments on Pope Leo X, 1842 reprint) and Paolo Cardinal Giovio (De Vita Leonis Decimi..., op. cit.), two associates who were witnesses to it."
Disputed

Man and Socialism in Cuba (1965)

Source: SPQR: A History of Ancient Rome

The Girl in Blue (1970)

Source: New Testament and Mythology and Other Basic Writings (1941), p. 9

To Colonel Theodor Pilling, Lieutenant Colonel Roger Michael, Major Winrich Behr in the evening of April 20, 1945. They tuned in the Wehrmacht receiver, and listened Joseph Goebbels's speech marking the Hitler's Birthday. Quoted in "Battle for the Ruhr" - Page 378 - by Derek S. Zumbro - 2006

Source: Obedience to Authority : An Experimental View (1974), p. 188
Context: Each individual possesses a conscience which to a greater or lesser degree serves to restrain the unimpeded flow of impulses destructive to others. But when he merges his person into an organizational structure, a new creature replaces autonomous man, unhindered by the limitations of individual morality, freed of humane inhibition, mindful only of the sanctions of authority.

The Last of the Mohicans (1826), Ch. 8